Since "X" represented the length of the shorter piece. The shorter piece is 3 feet long.
"2X +3" represented the length of the longer piece. Thus, the longer piece is calculated by substituting 3 in place of X and solve. 2(3) + 3 = 9 The longer piece of string is 9 ft long.In summary: short piece = 3 ft; long piece = 9ft